Means "The Special One", the most common nickname for Jose Mourinho, who is a world famous soccer manager (or coach depending on where you are from).

Mourinho is one hell of a manager, he has coached some of the most famous soccer teams in the world like Chelsea, Inter Milan, Real Madrid, and Porto! He's also won atleast 3 trophies for each team of these teams!
What makes him different from all other soccer coaches is that he's got the balls to say whatever he thinks, whether it's beaking other coaches or trashing the referee for making a bad call.

Starting in August 2013 he will be coaching Chelsea a second time.

Frank: Did you hear that TSO is coming back to Chelsea?
John: The Special One? You mean Jose Mourinho?
Frank: Yeah, definitely! Do you remember the last time that he was here? Chelsea were the kings of England!
John: I can't wait for him to get here, him and Chelsea are totally gonna whoop some ass!